1. Field of the Invention
The present invention relates to a liquid discharge head, a liquid discharge method and a liquid discharge apparatus, in which a change of state including generation of a bubble in a liquid is generated using thermal energy and the liquid is discharged from a discharge port in accordance with the change of state thereby to record. The present invention can be applied to devices such as a general printer, a copy machine, a facsimile including a communication system, and a word processor including a printer section, and further to an industrial recording device compositely combined with various kinds of processing units.
2. Related Background Art
A liquid discharge apparatus, particularly, an ink jet recording apparatus is ideal as a non-impact recording apparatus in modern business offices and other clerical work sections where quiet is required. Recently, from demands for higher density and higher speed recording properties and easier maintenance properties, further development and improvement of the ink jet recording head have been carried out. Particularly, in an ink jet recording apparatus using techniques disclosed in U.S. Pat. No. 4,723,129, a high density and high speed recording can be sufficiently performed by the structural feature. Therefore, the device is greatly supported in the market. Further, as one of techniques which can attain the high density and high speed for the recording head, U.S. Pat. No. 4,429,321 provides an ink jet recording head having a highly integrated structure.
On the other hand, to attain the recording of a high image quality using a recording head, which discharges only a desired discharge amount of droplets from a discharge port, the recording considerably depends on the providing density of heating elements of a recording head. That is, it uses a method of jetting ink to the same pixel position a plurality of times. This however invites problems such that the scanning times of the recording head are inevitably increased and a general printing speed is liable to decrease.
Japanese Patent Publication No. 62-48585 provides a multi-level output color ink jet recording head in which a plurality of heating elements are provided in one nozzle so that different discharge amounts of droplets can be discharged from a discharge port. This is, referred to as, so called, xe2x80x9cmulti-level heaterxe2x80x9d. For example, in the multi-level heater n heater elements are provided in one nozzle and are separately connected to a driver so that voltage can be independently applied to each of the heating elements. Further, the sizes of the heating elements are changed so that the heat release values are differentiated from each other in the respective heating elements in one nozzle. In this case, the recording dots by n heating elements are different from each other and {n Cnxe2x88x921+n Cnxe2x88x922+. . . +n C2+n C1+1} kinds of recording dots can be formed by the combination of simultaneously driven heating elements. That is, {n Cnxe2x88x921+n Cnxe2x88x922+ . . . +n C2+n C1+1} level gradation can be obtained with one nozzle.
However, since in the above-mentioned structure, a driving element such as a driving transistor or the like should be provided so as to correspond to the heating element by 1:1, a density n times greater than the nozzle density is required for the driving element to obtain {n Cnxe2x88x921+n Cnxe2x88x922+. . . +n C2+n C1+1} level gradation. Although a bipolar transistor and a N-MOS transistor have been used as a driving element for the heating element, one example of the area length of the driving element taken along a direction along the nozzle is about 70 xcexcm. In a case of, for example, 360 dpi recording head, a providing length of one driving element is 70/n xcexcm. If a recording head is a 720 dpi recording head, the length of 35/n xcexcm is required. As the result, to increase the density of the driving element, it is required to arrange a transistor at n steps or the like. In this case, control circuit wiring becomes complicated or the size of a recording head substrate must be enlarged. As the result, the structure is liable to lead to the increase of cost, and further, it becomes difficult to adapt the need of miniaturization of the recording head.
Incidently, with the use of a liquid discharge technology using thermal energy in many fields, in addition to the need for a higher image quality, a technology of satisfactorily discharging various liquids such as a high viscosity liquid or the like and a liquid discharging technology having a higher liquid discharge efficiency as compared to conventional technologies, are recently, increasingly desired. From such viewpoints various liquid discharge technologies are disclosed in, for example, Japanese Patent Publication No. 61-59916, Japanese Patent Application Laid-Open No. 55-81172, Japanese Patent Application Laid-Open No. 59-26270, and the like.
An object of the present invention is to provide a liquid discharge head, a liquid discharge method and a liquid discharge apparatus, in which a high gradation can be easily obtained and the simplification of a circuit arrangement and the miniaturization of a recording head can be attained without using a structure in which a plurality of heating elements are provided in one nozzle.
Another object of the present invention is to provide a liquid discharge head, a liquid discharge method and a liquid discharge apparatus, in which the volume of a droplet discharged is changed and a concentration change and a dot change on a recording medium can be realized by controlling the volume of a bubble generated in al liquid flow path.
Still another object of the present invention is to provide a liquid discharge head comprising a heat generating element for generating thermal energy which is used for discharging liquid from a discharge port, and a protective layer provided on the heat generating element to protect the heat generating element, wherein the protective layer has a first region with a substantially uniform and desired thickness and a second region with a substantially uniform thickness thinner than the desired thickness, the volume of liquid droplets discharged from the discharge port is changed by changing electric energy applied to the heat generating element.
Still another object of the present invention is to provide a liquid discharge head comprising a heat generating element for generating thermal energy which is used for discharging liquid from a discharge port, a protective layer provided on the heat generating element to protect the heat generating element and a moving member provided facing the heat generating element and having a free end which is displaced in accordance with generation of a bubble due to the thermal energy, wherein the protective layer has a first region with a substantially uniform and desired thickness and a second region with a substantially uniform thickness thinner than the desired thickness, the volume of liquid droplets discharged from the discharge port is changed by changing electric energy applied to the heat generating element.
Still another object of the present invention is to provide a liquid discharge method using a liquid discharge head having a heat generating element for generating thermal energy which is used for discharging liquid from a discharge port, and a protective layer for protecting the heat generating element, provided on the heat generating element, the protective layer having a first region with a substantially uniform and desired thickness and a second region with a substantially uniform thickness thinner than the desired thickness, wherein a size of a bubble generated on the heat generating element is changed by changing electric energy applied to the heat generating element while keeping a region of the starting point of bubbling to the second region, whereby the volume of liquid droplets discharged from the discharge port is changed.
Still another object of the present invention is to provide a liquid discharge method using a liquid discharge head having a heat generating element for generating thermal energy which is used for discharging liquid from a discharge port, a protective layer for protecting the heat generating element, provided on the heat generating element and a moving member provided facing the heat generating element and having a free end which is displaced in accordance with generation of a bubble due to the thermal energy, the protective layer having a first region with a substantially uniform and desired thickness and a second region with a substantially uniform thickness thinner than the desired thickness, wherein a size of a bubble generated on the heat generating element is changed by changing electric energy applied to the heat generating element while keeping a region of the starting point of bubbling to the second region, whereby the volume of liquid droplets discharged from the discharge port is changed.
According to the present invention the volume of a droplet discharged from one discharge port can be easily varied in a plurality of steps. Further a high gradation can be attained by selectively changing a signal inputted to one heat generating element without providing a plurality of heat generating elements in one nozzle. Further, since it is not necessary to arrange a heat generating element at a high density with necessary level, simplification of a circuit arrangement and miniaturization of a recording head can be attained. Additionally, since the present invention has a partially thin protective layer area, it has the effects that the consumption power necessary for obtaining an ordinary amount of liquid discharge can be further lowered than conventional cases.
The present invention provides the protective layer on the heat generation layer has stepwise a first region having a substantially uniform predetermined thickness and a second region having a uniform thickness smaller than the predetermined thickness. According to this arrangement, reaching temperatures at the regions for a predetermined applied energy are different for each other so that digital-like simple gradation recording can be obtained with high feasibility.